Swim fin



March 15, 1966 F. H. GWYNNE SWIM FIN Filed April 6, 1964 INVENTOR. H. GWWM.

A 77'0ENE Y United States Patent 3,239,857 SWIM FIN Frederick H. Gwynne, 250 W. 85th St., New York, NY. Filed Apr. 6, 1964, Ser. No. 357,530 6 Claims. (Cl. 9-309) This invention relates to swim fins and has as its primary object to provide a swim fin capable of enabling a swimmer to utilize .more effectively the potential strength of his large leg muscles and at the same time achieve relief from the fatigue ordinarily experienced in the foot of a user of conventional swim fins.

The greater part of the propelling thrust developed from a swim fin occurs during the kick stroke, or while the foot is everted or extended outwardly. During the kick stroke the fin blade is curved outwardly along its length and the action of the fin blade on the water as the leg is moved develops the maximum propelling force on the swimmer. The strain on the foot and ankle is greatest when the foot is disposed at or near the limit of its outward pivotal movement with respect to the leg. As is well understood, the propelling force on the water reacts through the cooperating bones and muscles of the foot and brings on local fatigue which limits the endurance of a swimmer and also his capacity to maintain a rapid rate of movement through the water.

It 'is among the objects of the present invention to provide a swim fin with which it is possible to develop greater thrust within the physical capacity of a given swimmer, and which is capable of prolonged use beyond the limit of endurance of a person using conventional swim fins.

The swim fin is so constructed as to transmit to the lower leg of a user some of the leverage forces which otherwise would be borne principally by the foot of one using a conventional swim fin, whereby to relieve the cooperating bones and muscles of the foot from bearing the full brunt of the reaction of the water during a power stroke. This is accomplished by providing a connection comprising a resilient hinge which extends across the ankle and connects with the fin blade and a casing which encircles the lower leg of a swimmer whereby to aid in resisting excessive bending of the foot outwardly beyond a tolerable extended position. The connection saves the foot from strain due to the full thrust of the water on the fin blade during a power stroke.

Further and other objects of the present invention will be hereinafter set forth in the accompanying specification and claims and demonstrated by the drawings which show by way of illlustration a preferred embodiment and the principle of my invention and what I now consider the best mode in which I have contemplated applying that principle. Other embodiments of the invention employing the same principle may be used and structural changes made as desired by those skilled in the art within the spirit of the appended claims and without departing from the present invention.

In the drawing:

FIG. 1 is a plan of a swim fin embodying the present invention;

FIG. 2 is a side elevation of the swim fin shown in FIG. 1;

FIG. 3 is a view of the underside of the shoe member of the swim fin as seen from line 3-3 of FIG. 2;

FIG. 4 is a detail showing a section of the fin blade on line 44 of FIG. 1;

FIG. 5 is a cross-sectional detail at line 55 of FIG. 2;

FIG. 6 is a cross-sectional detail at line 6-6 of FIG. 2;

FIG. 7 is a diagram illustrating the general disposition of the swim fin with respect to the leg of a user when the leg and foot are in an at rest position;

FIG. 8 is a diagram showing the general disposition of 3,239,857 Patented Mar. 15, 1966 "ice the swim fin with respect to a leg and foot when the foot is extended as in approaching the end of a power stroke.

The swim fin of the present invention includes a footreceiving member or shoe 10 having a substantially flat platform piece 11 and a vamp forming a socket 12 for containing the forepart of the foot of a swimmer. The foot is held forwardly on the platform by a heel portion 13 which rises from the platform and connects to opposite sides of the socket. The vamp is open at its forward end 14 to allow for freedom of the toes.

The web 15 of the fin blade 16 extends forwardly from the forcpart of the shoe 10. The side edges of the web are provided with flanges 17 and 18 which extend laterally above the upper surface of the web and laterally below its lower surface as shown in FIG. 4. The underside of the web is provided with a central rib 19. The flanges and rib are designed to allow gradually increasing flexibility of the fin blade from its emergence from the shoe 10' to the distal end of the fin blade. The normal unstrained angular position of the fin blade 16 with respect to the shoe 10 is generally illustrated in FIG. 2, although the angular relationship may be varied to suit the desire of a maker without materially affecting the function of the swim fin.

T-he socket member 12 is connected to a leg-encasing member 20 by a strip 21 extending along one side of the ankle, and by another strip 22 extending along the other side of the ankle. The connecting strips 21 and 22 are molded to conform to and lay against adjacent portions of the foot except in areas opposite the ankle where the inner sides of the material are sufficiently dished, as indicated at 24 and 25, FIG. 6, to avoid friction on the ankle bones.

The leg casing is formed to engage the lower part of the leg of a swimmer. The length of the leg casing 20 is preferably such that its upper end will reach no higher than just below the bulbous part of the calf muscle (gastrocnem-ius). The leg casing is split longitudinally so that it can be wrapped in firm engagement around the leg. Any kind of a buckle or other suitable engaging elements, such asja snap button 23, may be used to attach the casing to the leg.

The entire structure of the swim fin may be composed of rubber, or of any suitable rubber-like material. It can be molded in one piece or made from several pieces joined together to form a single integral article. The normal angular position of the leg casing 20 with respect to the shoe 10 corresponds to the angular relationship between the lower leg and the foot of a swimmer which is considered to be normal when the swimmers legs are at rest in the water. An approximately normal condition is illustrated in FIG. 2.

As shown in FIG. 2, the side flanges progressively diminish in depth from the forepart of the shoe towards the distal end of the fin blade and so provide for a gradual increase in flexibility toward the end of the fin blade and the greates stiffness along the forepart of the shoe where the stress on the fin blade is transmitted to the shoe.

In use, the flanges act to transmit a bending force on the fin blade to the shoe and leg casing 20 by virtue of their extension backwardly along the sides of the shoe and of the casing. The depths and hence the crosssections of the flanges diminish in their portions extending backward from alongside of the opposite sides of the socket 12 and of the connecting strips 20, 21, and across the ankle joint to adjacent the top of the leg casing 20.

The flanges serve as resilient hinges permitting deflection of the leg casing with respect to the shoe. The resilient connection thus afforded between the leg casing and the shoe offers gradually increasing resistance to the pivoting of the leg casing with respect to the shoe and therefore acts to counteract a large portion of the force of the water on the fin blade when a swimmers foot is in an extended position as during a power stroke.

As demonstrated in FIG. 7, the fin blade 16 is in a normal unflexed condition when the leg and foot are quiescent or in a state of rest. The curved portions 27 of the flanges 17, 18 are also disposed in their normal unflexed condition when the foot is relaxed as explained hereinabove in reference to FIG. 2.

The diagram of FIG. 8 illustrates a strained condition of the swim fin which occurs during a power stroke. In the diagram, the fin blade 16 is flexed as when a push on the water is effected by the downward movement of a leg. The normal curvature of the portions 27 of the flanges which extend between the leg casing and the shoe is shown as being in a nearly straight line. In this flexed condition the flanges transmit an appreciable portion of the propelling force exerted by the leg from the casing 20 to the fin blade 16. The strained condition of the flanges has the effect of preventing excessive deflection of the foot and attendant strain due to the tendency of the flanges to return to their normal curved condition, FIG. 7.

The connection between the shoe and the leg casing functions to assist the foot in bearing the full force of propulsion of the fin blade on the water during a power stroke. The stress transmitted through the connection relieves the foot from strain during a time when the strain is severest, with the result that a swimmer can endure greater sustained effort. As a consequence, the bin blade can be considerably longer than a conventional fin blade without unduly taxing the strength of the swimmer. This is because the additional energy required for manipulating the swim fin of greater area is derived to a greater extent from the larger muscles of the leg. I have obtained more propulsion effect with a fin blade twice as long as that of a conventional swim fin without increase of fatigue in the foot.

While the form of the swim fin herein shown and described is admirably adapted to fulfill the objects primarily stated, it is to be understood that it is not intended to confine the invention to the one form of embodiment herein disclosed, for it is susceptible of embodiment in various forms all coming within the scope of the claims which follow,

What is claimed is:

1. A swim fin comprising a shoe-like member having a substantially flat base for underlying the foot of a user, a socket for receiving the forepart of the foot and means for engaging the back of the heel of the foot, an elongated fin blade formed integral with said base and extending generally forward from said base to its distal end, a casing adapted to encircle a lower portion of a wearers leg, means connecting said casing to said shoelike member, and means for resiliently controlling the deflection of said shoe-like member with respect to said casing, said deflection-controlling means comprising flanges extending substantially parallel to the side edges of said fin blade and continuing along opposite sides of said socket and of said connecting means and upwardly onto said leg casing.

2. A swim fin as in claim 1 wherein the cross-section of said flanges diminishes from adjacent said socket toward each of the ends of the flanges.

3. A swim fin as in claim 1, wherein the thicker portions of said flanges are located opposite the forepart of the shoe.

4. A swim fin as in claim 1 wherein said leg casing and said socket are connected by strips of flexible material.

5. A swim fin as in claim 1 wherein the length of said leg casing as measured from the socket extends a distance on the leg of a wearer which is no greater than the distance from the wearers ankle to just below the bulbous part of the calf muscle of the wearer.

6. In a swim fin having a shoe-like member and a fin blade, a leg casing attached to the shoe, and means comprising a curved reinforcing member at either side of the shoe extending rearwardly and upwardly from the shoe and alongside said leg casing, said reinforcing member formed integrally with said shoe and said leg casing and being adapted to increasingly resist bending upon flexure of the shoe with respect to the leg casing.

References Cited by the Examiner UNITED STATES PATENTS 2,851,707 9/1958 Samuels 9-309 FOREIGN PATENTS 457,103 3/1928 Germany. 746,764 3/1956 Great Britain.

FERGUS S. MIDDLETON, Primary Examiner. 

6. IN A SWIM FIN HAVING A SHOE-LIKE MEMBER AND A FIN BLADE, A LEG CASING ATTACHED TO THE SHOE, AND MEANS COMPRISING A CURVED REINFORCING MEMBER AT EITHER SIDE OF THE SHOE EXTENDING REARWARDLY AND UPWARDLY FROM THE SHOE AND ALONGSIDE SAID LEG CASING, SAID REINFORCING MEMBER FORMED INTEGRALLY WITH SAID SHOE AND SAID LEG CASING AND BEING ADAPTED TO INCREASINGLY RESIST BENDING UPON FLEXURE OF THE SHOE WITH RESPECT TO THE LEG CASING. 